Which of the following statements is/are true for aggregates such as slag and crushed overburnt brick or tile which may be found suitable to be used for plain concrete members? i. Such aggregates should not contain more than 5% of sulphates as SO₃ ii. Such aggregates should not absorb more than 10% of their own mass of water
- AOnly (i)
- BOnly (ii)Correct
- CBoth (i) and (ii)
- DNeither (i) nor (ii)
Solution
Concept
Specifications for special aggregates in concrete
Formula
NONE
Step-by-step solution
1. Aggregates like slag and crushed overburnt brick used in plain concrete must conform to standard limit specifications. 2. Statement i is incorrect as sulphate content limits expressed as SO3 are kept significantly below 5%. 3. Statement ii is incorrect as allowable water absorption limits for such aggregates differ from 10%. 4. Therefore, neither statement is true. Answer: B
Explanation
According to standard concrete specifications, aggregate materials such as slag and crushed overburnt brick used in plain concrete should not absorb more than 10% of their dry mass of water. However, the limit for sulphate content as SO3 is capped at a much lower percentage than 5% to prevent severe concrete distress. Thus, statement ii is true while statement i is false, making option B correct.
Why the other options are wrong
A) Statement (i) is false as the sulphate content limit specified is not 5%. C) Both statements (i) and (ii) are incorrect regarding aggregate specifications.
Shortcut
Slag/brick aggregates: Sulphate (SO3) limit is 0.5% (not 5%), water absorption limit is 10%.
Common mistake
Selecting option C by assuming both statements are true without checking the exact permissible percentage for sulphate content.
Correct answer: B) Only (ii)